Edge illuminated photodiodes

ABSTRACT

This invention comprises plurality of edge illuminated photodiodes. More specifically, the photodiodes of the present invention comprise novel structures designed to minimize reductions in responsivity due to edge surface recombination and improve quantum efficiency. The novel structures include, but are not limited to, angled facets, textured surface regions, and appropriately doped edge regions.

CROSS-REFERENCE

The present application is a continuation of Ser. No. 12/760,342, filedon Apr. 14, 2010, which is a continuation of U.S. patent applicationSer. No. 11/849,623, filed on Sep. 4, 2007 and issued as U.S. Pat. No.7,728,367, which is a continuation of U.S. patent application Ser. No.11/383,485, filed on May 15, 2006 and issued as U.S. Pat. No.7,279,731.”

FIELD

The present specification discloses photodiodes having improvedoperational and structural characteristics. More specifically, thepresent specification discloses novel edge illuminated photodiodes, andapplications using the same, possessing high responsivity, enhancedquantum efficiency using n+ diffused region, and p+ textured region onsilicon, and InGaAs/InP substrates respectively.

BACKGROUND

Photodiodes comprise a plurality of electrode radiation-sensitivejunctions formed in semiconductor material. Within a photodiode, chargecarriers are created by light that illuminates the junction and photocurrent is generated dependent upon the degree of illumination.Photodiodes are used for detection of optical power and subsequentconversion of the same to electrical power. Operationally, photodiodesabsorb photons and charged particles, which facilitate detection ofincident optical power, thereby generating current proportional to theincident power.

Photodiodes are typified by the quantification of certaincharacteristics, such as electrical, optical, current (I), voltage (V),and noise. Electrical characteristics predominantly include shuntresistance, series resistance, junction capacitance, rise or fall timeand frequency response whereas optical characteristics includeresponsivity, quantum efficiency, non-uniformity, and non-linearity.Noise in photodiodes is generated by a plurality of sources including,but not limited to, thermal noise, quantum or photon or shot noise, andflicker noise.

In the semiconductor industry it is often desirable to increaselight-induced current of photodiodes in order to increase thesignal-to-noise ratio and thereby enhance photodiode sensitivity.Photodiode sensitivity is crucial in low light-level applications and istypically quantified by noise equivalent power (NEP) defined as theoptical power that produces a signal-to-noise ratio of unity at thedetector output. NEP is usually specified at a given wavelength and overa frequency bandwidth of 1 Hz and is therefore expressed in units ofW/Hz^(1/2).

Silicon photodiodes, essentially active solid-state semiconductordevices, are among the most popular photodetectors providing highperformance over a wide wavelength range. For example, siliconphotodiodes are sensitive to light in the wide spectral range,approximately 200*10⁻⁹ m to 1200*10⁻⁹ m, extending from deep ultravioletall the way through visible to near infrared. Additionally, siliconphotodiodes detect the presence or absence of minute light intensitiesthereby facilitating precise measurement of the same on appropriatecalibration. For instance, appropriately calibrated silicon photodiodesdetect and measure light intensities varying over a wide range, fromvery minute light intensities of below 10⁻¹³ watts/cm² to highintensities above 10⁻³ watts/cm².

Silicon photodiodes can be employed in an assortment of applicationsincluding, but not limited to, spectroscopy, distance and speedmeasurement, laser ranging, laser guided missiles, laser alignment andcontrol systems, optical free air communication, optical radar,radiation detection, optical position encoding, film processing, flamemonitoring, scintillator read out, environmental applications such asspectral monitoring of earth ozone layer and pollution monitoring, lowlight-level imaging, such as night photography, nuclear medical imaging,photon medical imaging, and multi-slice computer tomography (CT)imaging, security screening and threat detection, thin photochipapplications, and a wide range of computing applications.

Several problems exist with conventional photodiodes currently in use.In particular, for relatively short wavelength illumination, forinstance below 800 nm, edge-illuminated silicon photodiodes absorb lightvery strongly near the edge surfaces thereby leading to low responsivitydue to edge surface recombination. Likewise, controlling quantumefficiency, specifically in case of edge illuminated InGaAs/InPphotodiodes, still remains a challenge.

The prior art fails to describe edge illuminated photodiodes thatprovide for lesser susceptibility to surface recombination effects, andpossess high responsivity, and high quantum efficiency respectively.Consequently, there is still a need for photodiodes possessing highresponsivity and high quantum efficiency. More specifically, there isdemand for high responsivity edge illuminated silicon photodiodes havinglesser susceptibility to surface recombination effects, which in turn isaccountable for minimization of responsivity. Furthermore, high quantumefficiency edge illuminated InGaAs/InP photodiodes are also stillneeded.

SUMMARY

The present invention is directed toward photodiodes having improvedoperational and structural characteristics. In one embodiment, thepresent invention is a photodiode comprising a substrate with at least aplurality of facets, wherein said plurality of facets comprise aproximate facet substantially comprising a region doped with an impurityof a first conductivity type; a distant facet parallel to the proximatefacet; a top facet having an anode metallization region and having aregion proximate to said anode metallization region doped with animpurity of a second conductivity type; a bottom facet having a cathodemetallization layer; a left facet; and a right facet parallel to theleft facet.

In a second embodiment, the present invention is a photodiode comprisinga substrate with at least a plurality of facets, wherein said pluralityfacets comprise a proximate facet; a distant facet, having an inner faceand an outer face, parallel to the proximate facet; a top facet havingan anode metallization region and a textured region doped with animpurity of a selected conductivity type; a bottom facet, having aninner face and an outer face, parallel to the top facet and furthercomprising a cathode metallization layer; a left facet; a right facetparallel to the left facet; and an angled facet having an inner face andan outer face, wherein the inner face of said angled facet forms anangle with the inner face of said distant facet of greater than 90degrees.

In another embodiment, the present invention is a photodiode comprisinga substrate with at least a plurality of facets, wherein said pluralityfacets comprise a proximate facet; a distant facet, having an inner faceand an outer face, parallel to the proximate facet; a top facet having ametallization region, a region doped with an impurity of a firstconductivity type, and at least two regions doped with an impurity of asecond conductivity type wherein said second conductivity type isdifferent from said first conductivity type; a bottom facet, having aninner face and an outer face, parallel to the top facet and furthercomprising a metallization layer; a left facet; a right facet parallelto the left facet; and an angled facet having an inner face and an outerface, wherein the inner face of said angled facet forms an angle withthe inner face of said distant facet of greater than 90 degrees.

In another embodiment, the present invention is a photodiode comprisinga substrate having a first conductivity type, a top region, and a bottomregion; a metallization layer of the first conductivity type extendingthe length of the bottom region; a V-groove extending the width of saidtop region; an oxide layer extending the full length of the top region;a metallization region of a second conductivity type extending above thetop region and through said oxide layer; and a layer diffused with saidsecond conductivity type positioned below said oxide layer in the topregion and extending the length of said V-groove, wherein said layer isin physical communication with said metallization region of the secondconductivity type. Optionally, the photodiode has a layer of film coversthe top region and wherein said layer creates a substantially planarsurface above the V-groove.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features and advantages of the present invention will beappreciated, as they become better understood by reference to thefollowing detailed description when considered in connection with theaccompanying drawings:

FIG. 1 a is a perspective view of one embodiment of an edge illuminatedphotodiode;

FIG. 2 a is a perspective view of another embodiment of the edgeilluminated photodiode of the present invention;

FIG. 2 b depicts a flipped perspective view of the edge illuminatedphotodiode of FIG. 2 a;

FIG. 2 c, is a perspective view of another embodiment of an edgeilluminated photodiode of the present invention;

FIG. 2 d depicts two distinct stages, prior to and subsequent tophotochip dicing, using two schematic diagrams;

FIG. 3 a is a perspective view of another embodiment of the presentinvention, comprising PN-junctions on both the front and back surfaces;

FIG. 3 b is a schematic view of another embodiment of the presentinvention, comprising PN-junctions on both the front and back surfaces;

FIG. 3 c is a schematic view depicting PN-junctions and the depletionregion of another embodiment of the present invention;

FIG. 4 a is a schematic view of another embodiment of the presentinvention, comprising an interior V-groove;

FIG. 4 b is a schematic view of another embodiment of the presentinvention, comprising an interior V-groove and a layer of film; and

FIG. 5 is a schematic view of another embodiment of the presentinvention.

DETAILED DESCRIPTION

The invention described herein comprises a plurality of photodiodes,optionally constructed as a diode array, each comprising n+ diffusedregions, or angled facets and textured p+ regions. These photodiodeshave improved performance characteristics, including, but not limitedto, improved responsivity and enhanced quantum efficiency.

The photodiodes of the present invention can be constructed usingsemiconductor materials known to persons of ordinary skill in the art.In one embodiment, edge illuminated photodiodes are formed on photochipsof semiconductor materials, including, but not limited to, IndiumGallium Arsenide (InGaAs), Indium Phosphide (InP), or siliconrespectively. These photochips may be cuboidal in geometry possessing atleast a plurality of sides, also referred to as a face or facet.

In a first embodiment, the edge illuminated photodiode is incorporatedin a photochip having six distinct facets, namely proximate, distant,top, bottom, left, and right respectively. The proximate and distantfacets are substantially parallel to each other. The top and bottomfacets are substantially parallel to each other, and the left and rightfacets are substantially parallel to each other. The proximate facetsubstantially comprises an n+ diffused region. The bottom facetcomprises a cathode metallization layer. The top facet comprises tworegions, namely an anode metallization region and a p+ doped region. Thep+ doped region is juxtaposed to the anode metallization region.

In second embodiment, an edge illuminated photodiode is incorporated ina substrate having seven distinct facets. Six facets include aproximate, distant, top, bottom, left, and right facet, respectively.The proximate and distant facets are substantially parallel to eachother. The top and bottom facets are substantially parallel to eachother, and the left and right facets are substantially parallel to eachother. The seventh facet is formed at an angle to no less than twofacets, i.e., the distant and bottom facets, respectively. Preferablythe angle of formation, measured relative to the internal face of eachfacet (the sides facing the inside of the photodiode), is greater than90 degrees. More preferably, the angle of formation is 135 degrees.

In one embodiment, the top facet comprises two regions, namely an anodemetallization region and a p+ doped and textured region. The p+ region,juxtaposed to the anode metallization region, is textured to reducereflectance at this surface, thereby improving quantum efficiency of thephotodiode. The p+ region is preferably textured to form a plurality ofsquare base pyramids therein. Alternatively, the top facet comprisesthree regions: a p+ doped region and two n+ doped regions where theperipheral portion of both the n+ doped regions is delimited by ametallic plate. The bottom facet is comprises a cathode metallizationlayer.

The present invention is directed towards detector structures for anassortment of applications. More specifically, the present invention isdirected towards novel edge illuminated photodiodes, and applicationsusing the same, possessing high responsivity and enhanced quantumefficiency using n+ diffused region and p+ textured region for P on Nsilicon or p+ diffused region and n+ textured region for N on P siliconand InGaAs/InP substrates. Various modifications to the preferredembodiment will be readily apparent to those of ordinary skill in theart, and the disclosure set forth herein may be applicable to otherembodiments and applications without departing from the spirit and scopeof the present invention and the claims hereto appended. Thus, thepresent invention is not intended to be limited to the embodimentsdescribed, but is to be accorded the broadest scope consistent with thedisclosure set forth herein.

The present invention comprises several embodiments that provide forlesser susceptibility to surface recombination effects and reflectanceand absorption losses and further provides for enhanced responsivity andimproved quantum efficiency. In one embodiment, the present inventioncomprises an edge illuminated photodiode that incorporates an n+diffused region, which facilitates the minimization of edge surfacerecombination. Referring now to FIG. 1 a, photodiode 101 a is shown.Photodiode 101 a comprises photochip 100 a, which is made of a suitablesemiconductor material possessing apt geometrical specifications. Forexample, and by no way of limitation, photochip 100 a comprises siliconthat is cuboidal in geometry.

The cuboid (or rectangular parallelepiped) shaped photochip 100 a hassix distinct facets. For purposes of elucidation, the sides or facets ofphotochip 100 a have been enumerated as proximate 102 a, distant 104 a,top 104 a, bottom 105 a, left 106 a, and right 107 a. Persons ofordinary skill would appreciate that the present designation ofphotochip geometry is not limited to the description provided herein andcan be adjusted to suit other design, fabrication, and functionalspecifications.

A substantial portion of proximate facet 102 a comprises region 108 apossessing characteristics designed to improve responsivity and quantumefficiency. Region 108 a may be heavily doped, utilizing diffusion orimplant techniques, with a suitable dopant of a particular conductivitytype, such as p-type or n-type. In one preferred embodiment, an n-typedopant is used. Varieties of n-type dopants are known in this regard forinstance, phosphorus (P), arsenic (As), antimony (Sb), among others. Inone embodiment, the n+ doping layer is about 0.5 um to 1 um deep and canimprove quantum efficiency by about 50% to about 80% depending on thewavelength, i.e. improving by 80% at 550 nm and by 50% at 850 nm.

A substantial portion of proximate facet 102 a may be subjected tocontrolled n+ diffusion to generate an n+ diffused region 108 a. Thereare many different approaches available in the prior art to carry outdiffusion process, such as ion-implantation etc. However, the choice ofthe diffusion method is dependent on various factors, such as diffusioncoefficient of the dopant, permissible error in diffusion depth,diffusion source, among other variables. It must be noted that the taskstated above, such as diffusion, is routine undertaking of engineeringfor those of ordinary skill in the art having the benefit of thisdisclosure and, therefore, will not be further detailed herein.

The n+ diffused region 108 a assists in minimizing a reduction inresponsivity of photodiode chip 101 a. Typically, a reduction inresponsivity occurs due to edge surface recombination. The existence ofn+ diffused region 108 a helps generate an electric field thatfacilitates the repulsion of minority carriers, thereby minimizingrecombination. It is therefore preferred that, in the formation of n+diffused region 108 a, dopant concentration should significantly exceedphotogenerated carrier concentration. It must be noted that a heavilydoped region juxtaposed to a relatively lightly doped region forms ahigh low n+ n junction, which acts as a low recombination velocitysurface thereby facilitating minimization or reduction of surfacerecombination. Likewise, n+ diffused region 108 a juxtaposed to arelatively lightly doped bulk region, specifically portion of photochip100 a flanking n+ diffused region 108 a, forms an interface that acts asa low recombination velocity surface, thereby minimizing surfacerecombination.

Top facet 104 a comprises two regions, 114 a and 111 a. Region 114 a isessentially a heavily doped region. Region 114 a may be doped with anappropriate impurity or dopant of selected conductivity type, suchp-type or n-type. For instance, and by no way of limitation, a p-typedopant, such as boron, is preferred.

Region 111 a comprises an anode metallization region. Appropriate metalis utilized in the formation of anode metallization region. Forinstance, use of gold (Au) or aluminum (Al) is preferred. Metallizationcan be accomplished using any of a number of known approaches,including, for instance, subtractive processes, fully additiveprocesses, and semi-additive processes. Metallization is performed usingan assortment of techniques including, but not restricted to,evaporation, sputtering, plating, or electrolytic or electroless. Morespecifically, semiconductor devices employ metallization primarily toserve at least dual purpose: a) to form an electrical contact and b) toform an interconnection means within die circuits. Known processes makeuse of appropriate metals and/or alloys as materials for metallization.For instance, thin-film aluminum is most extensively exploited materialfor metallization and, due to low resistivity and adhesion compatibilitywith silicon dioxide, is very suitable for metallization. A disadvantageof aluminum as metallization material is low melting temperature, i.e.660° C., and low Al—Si eutectic temperature, i.e. 577° C. These restrictthe maximum processing temperature once the aluminum layer has beendeposited.

In one embodiment, bottom facet 105 a is subjected to metallization.Accordingly, bottom facet 105 a includes a cathode metallization layer109 a, which preferably comprises, but is not limited to, gold (Au).

In a second embodiment, the present invention comprises an edgeilluminated photodiode incorporated in a suitable semiconductorsubstrate with an angled facet and a textured p+ surface. The texturedp+ surface reduces reflectance thereby enhancing the quantum efficiencyof the photodiode.

Referring now to FIG. 2 a, an embodiment of an edge illuminatedphotodiode of the present invention is shown. Photodiode 201 a comprisesphotochip 200 a, which is made of a suitable semiconductor materialpossessing apt geometrical specifications. For example, and by no way oflimitation, photochip 200 a comprises silicon that is cuboidal ingeometry. The cuboid (or rectangular parallelepiped) shaped photochip200 a has six distinct facets. For purposes of elucidation, the sides orfacets of photochip 200 a have been enumerated as proximate 202 a,distant 204 a, top 204 a, bottom 205 a, left 206 a, and right 207 a.Persons of ordinary skill would appreciate that the present designationof photochip geometry is not limited to the description provided hereinand can be adjusted to suit other design, fabrication, and functionalspecifications.

Bottom surface 205 a is subjected to metallization in accord with theprinciples of the present invention. Consequently, bottom facet 205 acomprises a cathode metallization layer 208 a. For example, and by noway of limitation, the use of gold (Au) is preferred.

Top facet 204 a comprises two regions, 211 a and 214 a. Region 214 a isessentially a heavily doped region. Region 214 a may be doped with anappropriate impurity or dopant of selected conductivity type, suchp-type or n-type. For instance, and by no way of limitation, a p-typedopant, such as Zn in InP/InGaAs photodiodes and boron in siliconphotodiodes, is preferred. Region 211 a comprises an anode metallizationregion. Appropriate metal is utilized in the formation of anodemetallization region. For instance, use of gold (Au) or aluminum (Al) ispreferred.

In one embodiment, the amount of light absorbed by the semiconductorsubstrate is improved by modifying the photodiode surface. Twomechanisms are primarily accountable for the minimization or reductionof the amount of light absorbed by a photodiode. First, light may bereflected off the semiconductor substrate, i.e. reflection losses.Second, light may enter the substrate and exit without having beenabsorbed, i.e. absorption losses. Both of these loss mechanisms can becontrolled by the modifying the photodiode surface in an attempt toattain surface imperfections. Surface imperfections can be achieved viaroughening or texturing of the substrate surface.

Surface texture plays a vital role in facilitating confinement ortrapping of light within the photochip. Texture includes roughness,waviness, and lay, namely short wavelength deviations of a surface fromthe nominal surface. Surface texturization, or surface texturing, isresponsible for altering the transmission properties of semiconductorsurfaces within devices. Surface texturing facilitates 1) confinement ortrapping of light, and 2) reduces reflectance thereby improving thequantum efficiency of devices. For instance, reflection losses arediminished via increment in the probability that a light ray will strikethe substrate surface multiple times, whereas absorption losses arereduced via light confinement within the substrate body, called lighttrapping. Surface texturization of material is known to persons ofordinary skill in the art. In general, surface texturization is executedeither via isotropic (dissolution) or anisotropic etching.

Surface textured region 210 a is shown in FIG. 2 a and is furtherdetailed in FIG. 2 b. FIG. 2 b depicts a flipped perspective view of theedge illuminated InGaAs/InP photodiode 201 a of FIG. 2 a. In oneembodiment, region 210 b may be textured utilizing apt surface texturingtechniques, irrespective of the crystallographic orientation ofInGaAs/InP crystal, in an attempt to cause surface modificationsthereupon through the formation of a plurality of convexities andconcavities. These convexities and concavities possess appositegeometrical and dimensional specifications. For example, region 210 bmay be textured preferably forming a plurality of three-dimensional(3-D) square base pyramidal prisms therein. It must be noted here thatthe square base pyramidal prisms facilitate light trapping orconfinement within photodiode 201 b. In this regard, several texturingtechniques are known that do not rely on crystallographic orientation,including reactive ion etching.

Referring back to FIG. 2 a, a seventh facet 214 a is positioned betweentwo facets, preferably 204 a and 205 a. The seventh facet 214 a isangled relative to distant facet 204 a and bottom facet 205 a. The angleof formation between the inner face of the seventh facet 214 a and theinner face of distant facet 204 a is between 90 and 180 degrees,preferably around 135 degrees. The angle of formation between the innerface of the seventh facet 214 a and the inner face of bottom facet 205 ais between 90 and 180 degrees, preferably around 135 degrees.

Angled facet 214 a may be fabricated utilizing appropriate etchingtechniques. Typically, angled facets may be fabricated in an assortmentof ways including, but not restricted to, wet etching and dry etching. Aperson of ordinary skill in the art would know how to fabricate angledfacet 214 a.

In one embodiment, photodiode 201 a possesses the followingspecifications: device type is InP/InGaAs PIN photodiode; detectionrange varies from a minimum of approximately 800 nm to a maximum ofapproximately 1700 nm (i.e. optical bandwidth); active area diameter istypically 85 μm; operating voltage is typically −5 V; responsivity is ata minimum of approximately 0.70 A/W; dark current is <1 nA; reversebreakdown voltage is a minimum of 20 V; bandwidth is approximately 1GHz; capacitance is 1 pF (when measured @Vr=−5 V); operating temperaturevaries from a minimum of −40° C. to a maximum of 85° C.; chip size is350*350 μm typical; chip thickness is 200 μm typical; and detectablearea 75*35 μm. All parameters, discussed above, are applicable for achip temperature range of −40° C. to +85° C. and include any detrimentaleffects due to end of life (EOL) characteristics. The abovespecifications are merely for the purposes of elucidation, and are notlimiting. Various modifications to the disclosed embodiments will bereadily apparent to those of ordinary skill in the art, and thedisclosure set forth herein may be applicable to other embodiments andapplications without departing from the spirit and scope of the presentinvention and the claims hereto appended.

A third embodiment of an edge illuminated photodiode of the presentinvention is depicted in FIG. 2 c. Photodiode 201 c comprises photochip200 c, which is made of a suitable semiconductor material possessing aptgeometrical specifications. For example, and by no way of limitation,photochip 200 c comprises silicon that is cuboidal in geometry. Thecuboid (or rectangular parallelepiped) shaped photochip 200 c has sixdistinct facets. For purposes of elucidation, the sides or facets ofphotochip 200 c have been enumerated as proximate 202 c, distant 203 c,top 204 c, bottom 205 c, left 206 c, and right 207 c. Persons ofordinary skill would appreciate that the present designation ofphotochip geometry is not limited to the description provided herein andcan be adjusted to suit other design, fabrication, and functionalspecifications.

Bottom surface 205 a is subjected to metallization in accordance withthe principles of the present invention. Consequently, bottom facet 205a comprises a finish layer 220 c. For example, and by no way oflimitation, the use of gold (Au) is preferred.

Top facet 204 c comprises at least four regions, enumerated herein asfirst 208 c, second 209 c, third 210 c, and fourth 211 c. First region208 c is heavily doped, utilizing suitable diffusion techniques, with anapt impurity of the selected conductivity type, such as p-type orn-type. For instance, region 208 c is p+ doped. Region 208 c may bedoped with a p-type dopant selected the group including Zn or Be for InPmaterial and boron or gallium for silicon. In one embodiment, firstregion 208 c possesses the following specifications: dimensions(length*breadth) of approximately 75 μm*35 μm and the breadth-wisedistance of longer edge of first region 208 c from the distant edge oftop facet 204 c is 70 μm.

In one embodiment, region 208 c is textured using surface texturingtechniques to cause surface modifications thereupon. These convexitiesand concavities possess apposite three-dimensional (3-D) geometricalspecifications. For instance, this region 208 c is textured to form aplurality of square base pyramidal prisms therein. It must be noted herethat square base pyramidal prisms facilitate light trapping orconfinement within the photochip 200 c.

Second region 209 c is preferably subjected to anode metal platingtechniques. For example, and by no way of limitation, the use of gold(Au) as plating metal is preferred. Regions 210 c and 211 c are heavilydoped with an impurity of a selected conductivity type, such as p-typeor n-type. For example, regions 210 c and 211 c are preferably n+ doped.In one embodiment, a peripheral portion of regions 210 c and 211 c isdelimited by a length of cathode metal plating. For example, and by noway of limitation, the use of gold (Au) as cathode plating metal ispreferred.

Referring back to FIG. 2 c, a seventh facet 212 c is positioned betweentwo facets, preferably 203 c and 205 c. The seventh facet 212 c isangled relative to distant facet 203 c and bottom facet 205 c. The angleof formation between the inner face of the seventh facet 212 c and theinner face of distant facet 203 c is between 90 and 180 degrees,preferably around 135 degrees. The angle of formation between the innerface of the seventh facet 212 c and the inner face of bottom facet 205 cis between 90 and 180 degrees, preferably around 135 degrees. Angledfacet 212 c may be fabricated utilizing appropriate etching techniques.

Operationally, whenever a single mode fiber 250 c emanating light atwavelengths varying from a minimum of approximately 1300 nm to a maximumof approximately 1550 nm is positioned in vicinity of proximate facet202 c, comprising a detectable area (i.e. 75 μm*35 μm), light penetratesthrough the photodiode chip 201 c, gets reflected by angled edge 214 c,bends by 90°, and is incident on the textured p+ region 208 c. P+ regionis textured in an attempt to decrease reflectance at this surfacethereby improving quantum efficiency of photodiode 201 c.

In current embodiment, the photodiode 201 c may preferably possess thefollowing preliminary specifications: device type is InP/InGaAs PINphotodiode; detection range varies from a minimum of approximately 800nm to a maximum of approximately 1700 nm (i.e. optical bandwidth);active area diameter of about 85 μm; operating voltage of about −5 V;responsivity at a minimum of approximately 0.70 A/W; dark current is <1nA; reverse breakdown voltage is a minimum of 20 V; bandwidth is about 1GHz; capacitance is about 1 pF (when measured@Vr=−5 V); operatingtemperature varies from a minimum of −40° C. to a maximum of 85° C.;chip size is 350*350 μm typical; chip thickness is 200 μm typical; anddetectable area 75*35 μm. All parameters, discussed above, areapplicable for a chip temperature range of −40° C. to +85° C. andinclude any detrimental effects due to end of life (EOL)characteristics.

Another embodiment of the edge illuminated photodiode of the presentinvention is depicted in FIG. 2 d which illustrates two distinct stages:prior to, and subsequent to, photochip dicing. Photochip 200 d, prior todicing, comprises a photodiode 201 d having two primary regions, 202 dand 203 d. First region 202 d comprises alternating heavily dopedregions, such as 214 d and 216 d, doped with impurities of selectedconductivity types. For example, but not limited to such example, firstheavily doped region 214 d is doped with a suitable impurity of a firstselected conductivity, i.e. n-type, whereas second heavily doped region216 d is doped with a suitable impurity of a second selectedconductivity type, in opposition to first, i.e. p-type. Thesealternating heavily doped regions are positioned proximate to the frontside of device photochip 200 d.

In one embodiment, second region 204 d is in essence a passivation layerselectively grown atop front side of photochip 200 d. For example, useof materials including, but not limited to, silicon nitride, siliconoxide, silicon oxynitride or a layered combination of the aforementionedmaterials, etc. is preferred for the formation of the passivation layer.Regions 224 d and 226 d, which are devoid of the passivation layer andpositioned immediately atop heavily doped regions, 214 d and 216 drespectively, are preferably subjected to selective metallization.

The photodiode chip after photochip dicing is manufactured byeliminating region 218 d, shown in the photodiode chip before photochipdicing. To eliminate region 218 d, an initial v-groove 205 d ismanufactured in the photochip 200 d. Typically, the photochip 200 d isfirst coated with a layer of first masking material on its back side.Preferably, the first masking layer may be fabricated from materials,such as those of silicon dioxide (i.e. SiO.sub.2), or silicon nitride(i.e. Si.sub.3 N.sub.4). Although use only of certain masking materials,such as those of silicon dioxide or silicon nitride, has beenrecommended persons of ordinary skill would appreciate that theutilization of materials for the fabrication of the first masking layeris not limited to the aforesaid materials and can be changed to suitother requirements.

Once the first masking layer is applied to the back side of thephotochip, it is then superimposed with another conventional photoresistmask, thereby forming a second masking layer over the photochip. Usingany of conventional photolithographic techniques including, but notrestricted to, optical, UV (i.e. ultraviolet), EUV (i.e. enhancedultraviolet) photolithography, e-beam or ion-beam lithography, x-raylithography, interference lithography, etc. a pattern is rendered on thephotoresist mask or layer. The photoresist is exposed and developed,thereby exposing the photochip through the pattern. For instance, and byno way of limitation, use is made of a buffered hydrofluoric acid(i.e.H.F.sub.3) to etch the first masking layer preferably made ofSiO.sub.2. As an alternative, dry plasma gas etching can be used.

After the photoresist is locally removed and the first masking layersare etched, the photoresist is stripped off from the photochip and thephotochip subjected to anisotropic etching with, for example, a mixtureof HBR:H₂0₂:H₂0=1:1:3 can be used to create the V-groove in the InPlayer. Typically, the finished width of V-grooves can be controlled towithin 0.5 to 1 μm, such control being achieved using silicon nitridemasks and EDP as the etchant.

The first masking layer is then stripped off the photochip. Portions ofthe photochip through the pattern in the first masking layer aretypically, anisotropically etched to create the desired features (i.e.,the v-groove) that lie in the back side of photochip vicinal crystalplane. For example, and not intended to be limiting, use is made ofanisotropic etching technique to form the three dimensional v-groove onthe back side of the photochip 200 d at suitable position, such as 205d, as shown in FIG. 2 d. It must be noted here that inner wall ofV-groove 205 d is coated with an appropriate anti-reflective (AR) layer.For example, use of silicon nitride as AR layer is preferred. Afterdicing the photochip into dies, the region 218 d is automaticallyremoved.

Referring to FIG. 3A, in another embodiment, the present invention isdirected toward a photodiode 300 a having a top surface 315 a and abottom surface 345 a separated by p-type silicon 335 a. Locatedproximate to the top surface 315 a and bottom surface 345 a are p+regions 320 a and n+ regions 325 a. An anode metal layer 305 a is platedatop the p+ 320 a regions and a cathode metal layer 310 a is plated atopthe n+ regions 325 a. During operation, as also shown in FIG. 3C,depletion regions 330 a, 330 c form around the n+ regions 325 a, 325 cproximate to both the top 315 a and bottom surfaces 345 a, and betweenp+ region 320 a, 320 c. It is advantageous to have PN-junctions on boththe top and bottom surfaces for silicon side illuminated photodiodesoperated in relatively low reverse bias mode. While a p-type siliconregion 335 a is depicted having n+ depletion regions, it should beappreciated that the region types can be reversed, thereby having a n+type silicon region 335 a with p+ depletion regions.

Referring to FIG. 3B, in another schematic view of the embodiment inFIG. 3A, a photodiode 300 b having a top surface 315 b and a bottomsurface 345 b separated by p-type silicon 335 b is shown. Locatedproximate to the top 315 b and bottom 345 b surfaces are p+ 320 b and n+325 b regions. An anode metal layer 305 b is plated atop the p+ 320 bregions and a cathode metal layer 310 b is plated atop the n+ regions325 b. During operation, depletion regions 330 b form around the n+regions 325 b proximate to both the top 315 b and bottom 345 b surfaces.When a reverse bias is applied to both the top and bottom NP-junctions,the depletion regions extend quickly into the vertical direction andeventually merge together at a certain bias. The photogenerated carriersare collected immediately by the electric field of the extendeddepletion regions. Thus, the quantum efficiency, the speed of response,and the crosstalk are improved significantly.

In one embodiment, the distance between the centers of adjacent n+regions 325 b is approximately 170 μm, and the distance between thecenters of adjacent cathode metal layers 310 b is approximately 170 μm.In another embodiment, the distance between the edges of adjacent n+regions 325 b is approximately 50 μm. In yet another embodiment, thewidth of an n+ region 325 b is approximately 120 μm.

In another embodiment, the present invention comprises an edgeilluminated photodiode incorporated in a suitable semiconductorsubstrate with an interior placed V-groove. The interior placed V-groovereduces reflectance thereby enhancing the quantum efficiency of thephotodiode.

Referring now to FIG. 4 a, photodiode 401 a is shown. Photodiode 401 acomprises photochip 400 a, which is made of a suitable semiconductormaterial possessing apt geometrical specifications. For example, and byno way of limitation, photochip 400 a comprises silicon that is cuboidalin geometry. In one embodiment the photochip 400A comprises n-typesilicon.

Photodiode 401A comprises a top region 415A having an oxide layer 425Aand a V-groove 418A penetrating the width of the top region 415A.Photodiode 401A further comprises a bottom region 445A having a n+metallization layer 435A. Impinging within, and through, the oxide layer425A is at least one p+ metallization region 455A.

Immediately below the oxide layer 425A in the top region 415A are tworegions. The first region is a p+ diffused layer 408 a that extends fora portion of the length of the oxide layer 425A. The p+ layer 408Aassists in minimizing a reduction in responsivity of photodiode chip401A to incoming radiation 475A. The p+ layer does not extend the lengthof oxide layer 425A but does however, extend below the V-groove 418A inconjunction with the oxide layer 425A. The p+ layer is in physicalcommunication with the p+ metallization region 455A. The second regionis n-type silicon 409A.

Referring to FIG. 4B, the same photodiode of FIG. 4A is shown with theaddition of a layer of film 428B, such as clear polymide film or undopedsilica film. Photodiode 401B comprises a top region 415B having an oxidelayer 425B and a V-groove 418B penetrating the width of the top region415B. The addition of the layer of film 428B creates a substantiallyplanar region above the V-groove and serves to make the photodiode 401Bmore rugged. Photodiode 401B further comprises a bottom region 445Bhaving a n+ metallization layer 435B on top of a n+ diffused layer.Impinging within, and through, the oxide layer 425B is at least one p+metallization region 455B.

Immediately below the oxide layer 425B in the top region 415B are tworegions. The first region is a p+ diffused layer 408B that extends for aportion of the length of the oxide layer 425B. The p+ layer 408B assistsin minimizing a reduction in responsivity of photodiode chip 401B toincoming radiation 475B. The p+ layer does not extend the length ofoxide layer 425B but does however, extend below the V-groove 418B inconjunction with the oxide layer 425B. The p+ layer is in physicalcommunication with the p+ metallization region 455B. The second regionis n-type silicon 409B.

It should be appreciated that, since the p+ layer is created underneaththe V-groove, the depletion region of the PN-junction exists deep belowthe front surface of the photodiode chip; therefore, photo-generatedcarriers from a side illumination will collect before they have a chanceto recombine. Conversely, in a conventional photodiode 500 having a n+bottom layer 545, n+ metal layer 535, a p+ layer 518, an anti-reflectivelayer 528, a depletion region 508, a p+ metal contact 555, an oxidelayer 525, on n-type silicon 509, as shown in FIG. 5, photo-generatedcarriers 505, generated from a side illumination 575, have to travel amuch longer distance to the depletion region and, therefore, aresusceptible to carrier recombination loss.

It should be appreciated that the V-groove device of the presentinvention can be made more economically and efficiently than theembodiment depicted in FIG. 1 because the manufacturing process employsa wet KOH etch which is faster than the RIE etches required tomanufacture the embodiment of FIG. 1. It should also be appreciated thatthe selected conductivity type of the aforementioned regions could bereversed, i.e. the n-type silicon photochip could be p-type, the n+metallization layer could be p+, the p+ metallization region could ben+, and the p+ diffused layer in the top region could be n+, and stillfall within the scope of the present invention. It should also beappreciated that the exemplary dimensions and doping characteristics arenot limiting.

The photodiodes of the present invention can be employed in anassortment of applications including, but not limited to, spectroscopy,distance and speed measurement, laser ranging, laser guided missiles,laser alignment and control systems, optical free air communication,optical radar, radiation detection, optical position encoding, filmprocessing, flame monitoring, scintillator read out, environmentalapplications such as spectral monitoring of earth ozone layer andpollution monitoring, low light-level imaging, such as nightphotography, nuclear medical imaging, photon medical imaging, andmulti-slice computer tomography (CT) imaging, security screening andthreat detection, thin photochip applications, and a wide range ofcomputing applications.

The above discussion is aimed towards providing a preferred embodimentincorporating the novel aspects of the present invention and it shouldbe understood that the foregoing illustration is not the onlyapplication where the present invention can be reduced down to practice.The present invention can be suitably modified to incorporate otherpossible embodiments as well. The scope of the invention is definedsolely by the accompanying claims and within the scope of the claims;the present invention can be employed in various other situations. Forexample, circumstances wherein design and fabrication of edgeilluminated photodiodes possessing an assortment of figures of merit,quantitative or numerical measure of performance characteristics, forinstance, and by no way of limitation, low cost, economically,technically, and operationally feasible, high responsivity, high quantumefficiency using n+ diffused layer, p+ textured surface, and reliance ondiverse photochips, such as InGaAs/InP, silicon, etc. is desired whilestill staying within the scope of the present invention.

We claim:
 1. A photodiode for detecting wavelengths of light in a rangeof 800nm to 1700nm, comprising: a substrate defined by a proximatefacet, a distant facet, a bottom facet, and a top facet, wherein theproximate facet comprises a detectable area and is configured to firstreceive said wavelengths of light, wherein the distant facet is angledrelative to said proximate facet such that portions of said wavelengthsof light are reflected off said angled distant facet toward said topfacet, and wherein said top facet comprises a doped region.
 2. Thephotodiode of claim 1 wherein the doped region is a p+ region.
 3. Thephotodiode of claim 1 wherein the top facet comprises a textured p+doped region.
 4. The photodiode of claim 1 wherein the angled distantfacet reflects said wavelengths of light by 90 degrees.
 5. Thephotodiode of claim 1 wherein the angled distant facet forms an anglewith said bottom facet of greater than 90 degrees and less than 180degrees.
 6. The photodiode of claim 1 wherein the angled distant facetforms an angle with said bottom facet of 135 degrees.
 7. The photodiodeof claim 1 wherein the proximate facet comprises a region doped with animpurity of a first conductivity type.
 8. The photodiode of claim 1wherein the top facet has an anode metallization region.
 9. Thephotodiode of claim 8 wherein the bottom facet has a cathodemetallization layer.
 10. The photodiode of claim 1 wherein the top facethas an anode metallization region and has a region proximate to saidanode metallization region doped with an impurity of a secondconductivity type.
 11. The photodiode of claim 1 wherein the top facethas a metallization region, a region doped with an impurity of a firstconductivity type, and at least two regions doped with an impurity of asecond conductivity type wherein said second conductivity type isdifferent from said first conductivity type.
 12. The photodiode of claim1 wherein the bottom facet has a cathode metallization layer.